TUESDAY, May 17, 2005 (HealthDay News) -- Elaborate blood tests that look for genetic and biochemical abnormalities do nothing to predict whether someone who has had a life-threatening blood clot of the lung will have another, Dutch physicians report.
Instead, the risk that venous thromboembolism -- the formal name of the condition -- will happen again can be predicted by simple patient characteristics such as age, sex and whether a woman uses oral contraceptives.
Researchers at the Leiden University Medical Center report their findings in the May 18 issue of the Journal of the American Medical Association.
The Dutch team tracked outcomes in 474 patients who had a blood clot in the lung, following each patient's progress for an average of just over seven years. Ninety patients suffered a recurrent clot during that period of time.
As part of their research, the researchers also obtained blood samples from each patient, looking for genetic clotting abnormalities and elevated levels of several blood-clotting molecules to see whether these factors could predict clot recurrence.
These abnormalities "do not appear to play an important role in the risk of a recurrent thrombotic [clotting] event," the study authors concluded.
However, patient gender was a significant predictor, with men 2.7 times more likely than women to suffer a second clot. Older people were also more likely to have a recurrence, and the risk was higher for women taking oral contraceptives.
Patients whose clots occurred for no apparent reason were nearly twice as likely to have a second clot than those whose initial events were caused by some identifiable adverse event in the body, the researchers added.
The apparent uselessness of genetic testing in predicting clotting risk is an "ironic" finding, said Dr. Samuel Goldhaber, director of the venous thromboembolism research group at Brigham and Women's Hospital in Boston, since the Leiden team "is the group that put genetic testing on the map." In fact, the best known genetic marker for clotting problems is called the "Leiden gene," he noted.
"What they are saying now is that the circumstances of a venous thromboembolism are much more important than genetic testing," Goldhaber said. "Genetic tests may be important to us for academic reasons or for family interventions [prevention in near relatives], but the clinical setting has the greatest importance."
The report came as no surprise to Goldhaber. A number of studies with similar results have been reported at medical meetings and will soon appear in medical journals, he said, with implications for medical practice.
"In terms of clinical practice, the health-care professional needs to pay a lot more attention to the circumstances of a pulmonary embolism," he said. "Is there something that provoked it, or did it come out of the blue? The answers to these questions are much more important than fancy blood testing."
Dr. Jack E. Ansell, a professor of medicine at Boston University School of Medicine, said "the bottom line of the report is that an extensive work-up looking for underlying risk factors is not warranted for these patients."
But while such testing might have little immediate value in treating the patient, "they may be important in knowing a family's pedigree and what it means to a sibling, or to a female relative who uses oral contraceptives," Ansell said.
Still, genetic tests might yet be worthwhile for some patients, he said. "Some studies indicate that some genetic abnormalities might be associated with a slightly increased risk of recurrence," he said. "You must look at each individual, and determine what are the benefits of such an evaluation."
Dr. Clive Kearon, head of the clinical thrombosis unit at McMaster University in Hamilton, Ontario, called the study "useful and valuable" because of the number of factors it looked at and the length of the follow-up.
The study has some weaknesses, such as a lack of participants over the age of 70, Kearon said, but it reinforces a growing trend about testing. "It will cause some people discomfort, but the medical community is coming around to the view that [these] blood tests are not valuable," he said.
The full story of clots and stroke is available at the American Stroke Association.